The type of device with which this invention is concerned has disks pivotally mounted in approximately their median plane, contrastingly colored on opposite sides and carrying a permanent magnet having an axis with a component transverse to the pivot axis. A selectably reversible field forming means external to the disk controls the orientation of the disk by the influence of the field on the permanent magnet and causes it to display one or the other of its contrasting faces in the viewing direction.
Such disks are frequently arranged in columns and, in such columns are frequently arranged in a single frame. To obtain greater visibility for the disks of the display, it is sometimes desireable to make the disk oval instead of circular with its long dimension corresponding generally to the longitudinal direction of the column of the array. If the pivot axis is then directed in the column direction so that the pivot axes of all the disks in a column are coaxial, then the disk spindles and the spindle wells for the disks require space between adjacent disks in the column and such space detracts from the appearance of the display since it decreases the area of the display which may be reversed in appearance.